The automotive industry is required to limit certain emissions generated by engines when in use due to the adverse affect such emissions can have on human health and the environment. Such emissions include hydrocarbons, nitrogen oxides, sulphur oxides, carbon monoxide and particulate matter (PM).
One example of an exhaust treatment system component that helps enable the automotive industry to meet emission standards is the Johnson Matthey CRT® system. This technology (disclosed in EP 0 341 832) makes use of a process for combusting diesel particulate deposited on a filter in nitrogen dioxide at up to 400° C., which nitrogen dioxide is obtained by oxidising nitrogen monoxide in the exhaust gas over a suitable catalyst disposed upstream of the filter. The nitrogen monoxide oxidation catalyst can comprise a platinum group metal such as platinum, palladium, ruthenium, rhodium or combinations thereof. The filter can be coated with material that facilitates higher temperature combustion such as a base metal catalyst, e.g. vanadium oxide, La/Cs/V2O5 or a precious metal catalyst.
However, in an effort to continually reduce the adverse effect of engine emissions governments are adopting increasingly strict emission standards, e.g. according to European Union emission standards a diesel powered passenger car produced in 1993 was allowed to produce up to 0.140 g/km of PM (the so-called Euro I Tier Emission Standard), whereas in 2005 the regulated amount was no more than 0.025 g/km of PM (Euro IV Tier) and it is anticipated Euro V Tier could be 0.005 g/km. Therefore an exhaust treatment system that was able to meet the emission standards set for vehicles five years ago is not necessarily capable of meeting the emission standards set to be introduced in the near future. Hence new exhaust treatment systems constantly need to be developed to enable the automotive industry to meet the progressively stricter emission standards. However, as with the development of any new system (or component of a system) such a system needs to be tested in the laboratory before it is put to use in practice. Many tests might be carried out on an exhaust treatment system comprising a catalyst and/or a filter before the system is put into practice, such tests including durability testing, catalyst ageing, filter retention tests, pressure drop loading tests, ageing cycles with regeneration tests, NOx-trap regeneration, soot mass limit tests, poison testing (including sulphation ageing, and testing to see how the catalyst and/or filter reacts to exposure to a range of chemicals such as phosphates, halides, alkaline earth and rare earth compounds), ash loading studies, white smoke tests and the testing of a system when the engine is fuelled with a variety of alternative fuels. Those organisations carrying out such tests include: exhaust system manufacturers (including filter manufacturers, coating companies and canning companies), vehicle manufacturers, consultancies, research institutions and academic laboratories.
Prior art methods of laboratory testing a new exhaust system tend to rely on the use of a bench-mounted vehicular internal combustion engine for prolonged periods of time, which is exceedingly costly. Nonetheless, since it is important that the testing of such a system should mimic the conditions under which the system would be used in practice, and that the PM contacting the system mimic the PM produced by an engine, no reliable alternative was previously available.
DE 37 10 749 C1 discloses an apparatus for simulating deposits of foreign substances contained in gaseous media on functional parts in flow systems, such as the deposit of soot in the air intake systems of engines. EP 1 616 914 A1 discloses an apparatus for producing carbon black with defined properties and for testing filters by passing a gas stream containing carbon black through a filter.